Increasing the memory performance of flash memory devices by writing sectors simultaneously to multiple flash memory devices

ABSTRACT

In one embodiment of the present invention, a memory storage system for storing information organized in sectors within a nonvolatile memory bank is disclosed. The memory bank is defined by sector storage locations spanning across one or more rows of a nonvolatile memory device, each the sector including a user data portion and an overhead portion. The sectors being organized into blocks with each sector identified by a host provided logical block address (LBA). Each block is identified by a modified LBA derived from the host-provided LBA and said virtual PBA, said host-provided LBA being received by the storage device from the host for identifying a sector of information to be accessed, the actual PBA developed by said storage device for identifying a free location within said memory bank wherein said accessed sector is to be stored. The storage system includes a memory controller coupled to the host; and a nonvolatile memory bank coupled to the memory controller via a memory bus, the memory bank being included in a nonvolatile semiconductor memory unit, the memory bank has storage blocks each of which includes a first row-portion located in said memory unit, and a corresponding second row-portion located in each of the memory unit, each of the memory row-portions provides storage space for two of said sectors, wherein the speed of performing write operations is increased by writing sector information to the memory unit simultaneously.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of our prior co-pending U.S.application Ser. No. 10/071,972, filed on Feb. 5, 2002 and entitled“Increasing the Memory Performance of Flash Memory Devices by WritingSectors Simultaneously to Multiple Flash Memory Devices”, which is acontinuation of our prior U.S. application Ser. No. 09/705,474, filed onNov. 2, 2000 now U.S. Pat. No. 6.397,314 and entitled “Increasing theMemory Performance of Flash Memory Devices by Writing SectorsSimultaneously to Multiple Flash Memory Devices”, which is acontinuation of our prior U.S. application, Ser. No. 09/487,865 filed onJan. 20, 2000, now U.S. Pat. No. 6,202,138 entitled “Increasing theMemory Performance of Flash Memory Devices by Writing SectorsSimultaneously to Multiple Flash Memory Devices”, which is acontinuation of application Ser. No. 09/030,697 filed on Feb. 25, 1998,now U.S. Pat. No. 6,081,878 entitled “Increasing the Memory Performanceof Flash Memory Devices by Writing Sectors Simultaneously to MultipleFlash Memory Devices”, which is a continuation-in-part of U.S. patentapplication Ser. No. 08/946,331 filed Oct. 7, 1997, now U.S. Pat. No.5,930,815, issued on Jul. 27, 1999, entitled “Moving Sequential SectorsWithin a Block of Information In a Flash Memory Mass StorageArchitecture”, which is a continuation-in-part of U.S. patentapplication Ser. No. 08/831,266 filed Mar. 31, 1997, now U.S. Pat. No.5,907,856 issued on May 25, 1999, entitled “Moving Sectors Within aBlock of Information In a Flash Memory Mass Storage Architecture”, whichis a continuation-in-part of U.S. patent application Ser. No. 08/509,706filed Jul. 31, 1995, now U.S. Pat. No. 5,845,313, issued on Dec. 12,1998, entitled “Direct Logical Block Addressing Flash Memory MassStorage Architecture”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of digital systems, such as personalcomputers and digital cameras, employing nonvolatile memory as massstorage, for use in replacing hard disk storage or conventional film.More particularly, this invention relates to an architecture forincreasing the performance of such digital systems by increasing therate at which digital information is read from and written to thenonvolatile memory.

2. Description of the Prior Art

With the advent of higher capacity solid state storage devices(nonvolatile memory), such as flash or EEPROM memory, many digitalsystems have replaced conventional mass storage devices with flashand/or EEPROM memory devices. For example, personal computers (PCs) usesolid state storage devices for mass storage purposes in place ofconventional hard disks. Digital cameras employ solid state storagedevices in cards to replace conventional films.

FIG. 1 shows a prior art memory system 10 including a controller 12,which is generally a semiconductor (or integrated circuit) device,coupled to a host 14 which may be a PC or a digital camera. Thecontroller 12 is further coupled to a nonvolatile memory bank 16. Host14 writes and reads information, organized in sectors, to and frommemory bank 16 which includes a first nonvolatile memory chip 18 and asecond nonvolatile memory chip 20. Chip 18 includes: an I/O register 22having a port 24 connected to a port 26 of controller 12 via a first bus28 which includes 8 bit lines; and a storage area 30 coupled with I/Oregister 22. Chip 20 includes: an I/O register 32 having a port 34connected to a port 36 of controller 12 via a second bus 38 whichincludes 8 bit lines; and a storage area 40 coupled with I/O register32. The first and second buses 28, 38 are used to transmit data,address, and command signals between the controller and the memory chips18 and 20. The least significant 8 bits (LSBs) of 16 bits of informationare provided to chip 18 via the first bus 28, and the most significant 8bits (MSBs) are provided to the chip 20 via the second bus 38.

Memory bank 16 includes a plurality of block locations 42 each of whichincludes a plurality of memory row locations. Each block location of thememory bank is comprised of a first sub-block 44 located in the firstnon-volatile memory chip, and a corresponding second sub-block 46located in the second non-volatile memory chip. Each memory row locationincludes a first row-portion 48 and a corresponding second row-portion50. In the depicted embodiment each of the first and second row-portions48 and 50 includes storage for 256 bytes of data information plus anadditional 8 bytes of storage space for overhead information. Where asector includes 512 bytes of user data and 16 bytes of non-user data(the latter commonly referred to as overhead information), 256 bytes ofthe user data and 8 bytes of the overhead information of the sector maybe maintained in the first row portion 48 of chip 18 and the remaining256 bytes of user data and remaining 8 bytes of overhead information ofthe same sector may be maintained in the second row portion 50 of chip20. Thus, half of a sector is stored in a memory row location 48 of chip18 and the other half of the sector is stored in memory row location 50of chip 20. Additionally, half of the overhead information of eachstored sector is maintained by chip 18 and the other half by chip 20.

In general, reading and writing data to flash memory chips 18 and 20 istime consuming. Writing data to the flash memory chips is particularlytime consuming because data must be latched in I/O registers 22 and 32,which are loaded 1 byte at a time via the first and second buses, andthen transferred from the I/O registers 22 and 32 to the memory cells ofthe flash memory chips 18 and 20 respectively. The time required totransfer data from the I/O registers to memory, per byte of data, isproportional to the size of the I/O registers and the size of the flashmemory chip.

During a write operation, controller 12 writes a single sector ofinformation to memory bank 16 by: (1) transmitting a write commandsignal to each of chips 18 and 20 via buses 28 and 38 simultaneously;(2) transmitting address data to chips 18 and 20 specifyingcorresponding sub-blocks 44 and 46 of the chips via buses 28 and 38simultaneously; and (3) sequentially transmitting a byte of user data toeach of chips 18 and 20 via buses 28 and 38 simultaneously for storagein the corresponding sub-blocks 44 and 46. The problem with such priorart systems is that while two bytes of information are written and readat a time, only one sector of information is accommodated at a time bythe memory bank 16 during a write command initiated by the host 14.

Another prior art digital system 60 is shown in FIG. 2 to include acontroller 62 coupled to a host 64, and a nonvolatile memory bank 66 forstoring and reading information organized in sectors to and fromnonvolatile memory chip 68, included in the memory bank 66. While notshown, more chips may be included in the memory bank, although thecontroller, upon command by the host, stores an entire sector in onechip. A block, such as block 0, includes 16 sectors S0, S1, . . . , S15.Also included in the chip 68 is an I/O register 70, which includes 512bytes plus 16 bytes, a total of 528 bytes, of storage space. Thecontroller transfers information between host 64 and memory 66 a byteat-a-time. A sector of 512 bytes of user data plus 16 bytes of overheadinformation is temporarily stored in the I/O register during a writeoperation and then transferred to one of the blocks within the memorydevice for storage thereof. During a read operation, a sector ofinformation is read from one of the blocks of the memory device and thenstored in the I/O register for transfer to the controller An importantproblem with the prior art architecture of FIG. 2 is that while a totalof 528 bytes may be stored in the I/O register 36, only one byte ofsector information may be transferred at a time between the controllerand the memory bank thereby impeding the overall performance of thesystem.

Both of the prior art systems of FIGS. 1 and 2 maintain LBA to PBAmapping information for translating a host-provided logical blockaddress (LBA) identifying a sector of information to a physical blockaddress (PBA) identifying the location of a sector within the memorybank. This mapping information may generally be included in volatilememory, such as a RAM, within the controller, although it may bemaintained outside of the controller.

FIG. 3 shows a table diagram illustrating an example of an LBA-PBA map300 defined by rows and columns, with each row 302 being uniquelyidentified, addressed, by a value equal to that of the LBA received fromthe host divided by 16. The row numbers of FIG. 3 are shown usinghexadecimal notation. Thus, for example, row 10H (in Hex.) has anaddress value equal to 16 in decimal. Each row 302 of map 300, includesa storage location field 304 for maintaining a virtual PBA value, an‘old’ flag field 306, a ‘used’ flag field 308, and a ‘defect’ flag field310. The flag fields provide information relating to the status of ablock of information maintained within the memory bank (in FIGS. 1 and2). The virtual PBA field 304 stores information regarding the locationof the block within the memory bank.

FIG. 4 shows a table diagram illustrating an exemplary format forstorage of a sector of data maintained in a memory bank. The virtual PBAfield 304 (FIG. 3) provides information regarding the location of ablock 400 of information with each block having a plurality of sectors402. Each sector 402 is comprised of a user data field 404, an ECC field406, an ‘old’ flag field 408, a ‘used’ flag field 410 and a ‘defect’flag field 412.

A further problem associated with prior art systems of the kinddiscussed herein is that the table 300 (in FIG. 3) occupies much ‘realestate’ and since it is commonly comprised of RAM technology, which isin itself costly and generally kept within the controller, there issubstantial costs associated with its manufacturing. Furthermore, aseach row of table 300 is associated with one block of information, thelarger the number of blocks of information, the larger the size of thetable, which is yet an additional cost for manufacturing the controllerand therefore the digital system employing such a table.

What is needed is a digital system employing nonvolatile memory forstorage of digital information organized in sector format for reducingthe time associated with performing reading and writing operations onthe sectors of information thereby increasing the overall performance ofthe system while reducing the costs of manufacturing the digital system.

SUMMARY OF THE INVENTION

It is an object of the present invention to increase the performance ofa digital system having a controller coupled to a host for operating anonvolatile memory bank including one or more nonvolatile memorydevices, such as flash and/or EEPROM chips, by reducing the timeassociated with reading and writing information to the nonvolatilememory bank.

It is another object of the present invention, as described herein, todecrease the time associated with storing sectors of information bywriting at least two sectors of information to at least two nonvolatilememory semiconductor devices during a single write command initiated bythe host.

It is another object of the present invention as described herein todecrease the time associated with reading sectors of information byreading at least two sectors of information from at least twononvolatile memory semiconductor devices during a single read commandinitiated by the host.

It is a further object of the present invention to store overheadinformation associated with two sectors of information in one of the twononvolatile memory semiconductor devices.

It is yet another object of the present invention to simultaneouslyaccess two bytes of a sector of information stored within twononvolatile memory devices thereby increasing the rate of performance ofa system employing the present invention by an order of magnitude of atleast two.

It is yet another object of the present invention to access one byte ofa first sector and one byte of a second sector of informationsimultaneously within two nonvolatile memory devices thereby increasingthe rate of performance of a system employing the present invention.

It is a further object of the present invention to reduce the size of avolatile memory table, or map, that maintains translations between thehost-provided sector addresses to addresses of blocks within thenonvolatile memory devices thereby reducing the cost of manufacturingthe digital system.

Briefly, the present invention includes a digital system having acontroller semiconductor device coupled to a host and a nonvolatilememory bank including a plurality of nonvolatile memory devices. Thecontroller transfers information, organized in sectors, with each sectorincluding a user data portion and an overhead portion, between the hostand the nonvolatile memory bank and stores and reads two bytes ofinformation relating to the same sector simultaneously within twononvolatile memory devices. Each nonvolatile memory device is defined bya row of memory locations wherein corresponding rows of at least twosemiconductor devices maintain two sectors of information therein withthe overhead information relating to the two sectors maintained in oneof the memory rows of the nonvolatile memory device. Each 32 sectors ofinformation defines a block identified by a virtual physical blockaddress with a block of information expanding between two memory deviceswherein an even and an odd byte of a sector is simultaneously read fromor written to two nonvolatile memory devices. In another embodiment, thecontroller stores an entire sector of information within a singlenonvolatile memory device and reads from or writes to, a sector ofinformation by processing corresponding bytes of at least two sectors intwo nonvolatile memory devices simultaneously.

These and other objects and advantages of the present invention will nodoubt become apparent to those skilled in the art after having read thefollowing detailed description of the preferred embodiments illustratedin the several figures of the drawing.

IN THE DRAWINGS

FIG. 1 is a block diagram of a prior art memory system in which a singlesector of information is written, two bytes at a time during a writeoperation, to a memory bank including two memory units each havingcapacity to store 256 bytes of user data in a single row location.

FIG. 2 is a block diagram of a prior art memory system in which a singlesector of information is written, one byte at a time during a writeoperation, to a memory bank including at least one memory unit havingcapacity to store 512 bytes of user data in a single row location.

FIG. 3 is a table diagram illustrating an exemplary map for translatinga host-provided logical block address (LBA) identifying a sector ofinformation to a physical block address (PBA) identifying a location forthe sector within a memory bank.

FIG. 4 is a table diagram illustrating an exemplary format for storageof a sector of data maintained in a memory bank.

FIG. 5 is a generalized block diagram of a memory system in accordancewith the present invention in which two sectors of information arewritten, two bytes at a time during a single write operation, to amemory bank including at least two memory units each having capacity tostore 512 bytes of user data in a single row location.

FIG. 6 is a detailed block diagram of the memory system of FIG. 5.

FIG. 7 is a table diagram generally illustrating a memory storage formatfor storing a block, including 32 sectors, of information in a memorybank including two non-volatile memory units wherein an even sector andan odd sector are stored in a single memory row location and whereineven data bytes of both sectors are stored in a row portion located in afirst of the memory units and odd data bytes of both sectors are storedin a second row portion located in the second of the memory units.

FIG. 8A is a table diagram generally illustrating organization of anexemplary LBA-PBA map for use in accordance with the present invention.

FIG. 8B shows a block diagram illustrating formats of addressinformation identifying sectors and associated blocks of information inaccordance with the present invention.

FIG. 9 is a timing diagram illustrating the timing of control, address,and data signals for a write operation performed by the memory system ofFIG. 6 wherein two sectors of information are simultaneously written,during a single write operation, to a memory bank having the memorystorage format illustrated in FIG. 7.

FIG. 10 is a table diagram illustrating a memory bank having a memorystorage format as depicted in FIG. 7 wherein a single sector is writtento a particular memory row location of the memory bank.

FIG. 11 is a table diagram illustrating a memory bank having analternative memory storage format as depicted in FIG. 7 wherein a singlesector is written to a particular memory row location of the memorybank.

FIG. 12 is a flowchart illustrating a process of simultaneously writingtwo sectors of information to two memory units during a single writeoperation in accordance with the present invention.

FIG. 12a shows a flow chart of the steps performed in executing thedefect management routine of FIG. 12.

FIG. 13 is a table diagram generally illustrating an alternative memorystorage format for storing a block, including 32 sectors, of informationin a memory bank including two non-volatile memory units wherein an evensector and an odd sector are stored in a single memory row location andwherein an even sector is stored in a first row portion located in afirst of the two memory units and an odd sector is stored in a secondrow portion located in the second of the two memory units.

FIG. 14 shows a timing diagram illustrating the timing of control,address, and data signals for a process of erasing a block of a memorybank in accordance with principles of the present invention.

FIG. 15 is a flowchart illustrating a process of erasing a block,including a first sub-block stored in a first memory unit and a secondsub-block stored in a second memory unit, in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 5 shows a generalized block diagram at 500 of a memory system inaccordance with principles of the present invention. The system includesa memory card 502 coupled to a host system 504. In one embodiment, host504 is a digital camera and memory card 502 is a digital film card, andin another embodiment, host 504 is a personal computer system and memorycard 502 is a PCMCIA card. Memory card 502 includes: a non-volatilememory bank 506 including a plurality of non-volatile memory units 508for storing sectors of information organized in blocks; a memorycontroller 510 coupled to the memory bank via a memory bus 512, andcoupled to the host 504 via a host bus 514. Memory controller 510controls transfer of sector-organized information between host 504 andmemory bank 506. Each sector of information includes a user data portionand an overhead portion. The memory controller performs write and readoperations, in accordance with the present invention, to and from thememory units of the memory bank as further explained below.

In the present invention, the non-volatile memory bank 506 may includeany number of non-volatile memory units 508 while in a preferredembodiment, the non-volatile memory bank has an even number of memoryunits. Also in the preferred embodiment, each of the non-volatile memoryunits is a flash memory integrated circuit device.

FIG. 6 shows a detailed block diagram at 600 of the memory system ofFIG. 5. Controller 510 is shown to include: a host interface 610connected to the host 504 via host bus 514 for transmitting address,data, and control signals between the controller and the host; a databuffer 614 having a port 616 coupled to a port 618 of the hostinterface; a microprocessor 620 having a port 622 coupled to a port 624of the host interface; a code storage unit 626 having a port 628 coupledto a port 630 of the microprocessor; a boot ROM unit 632 having a port634 coupled to port 630 of the microprocessor and to port 628 of thecode storage unit; a space manager 636 having a port 638 coupled to aport 640 of the microprocessor; a flash state machine 642 including aport 644 coupled to a port 646 of the microprocessor, a port 648 coupledto a port 650 of the space manager, and a port 645 coupled to a port 647of the data buffer; a memory input/output unit 652 having a port 654coupled to a port 656 of the flash state machine; an error correctioncode logic unit (ECC logic unit) 660 having a port 662 coupled to a port664 of the flash state machine, and a port 666 coupled to a port 668 ofthe data buffer 614.

In the depicted embodiment, memory bank 506 includes two non-volatilememory units (although additional memory units may be included, only twoare shown for simplicity); a first flash memory chip 670 designatedFLASH0 and a second flash memory chip 672 designated FLASH1. First flashmemory chip 670 includes a first input/output register (first I/Oregister) 671 and a storage area 669. Second flash memory chip 672includes a second input/output register (second I/O register) 673 and astorage area 674.

Memory bus 512 is used to transmit address, data, and control signalsbetween the controller 510 and memory bank 506. Memory bus 512 includesa flash bus 675 connected to a port 676 of memory I/O unit 652 fortransmitting address, data, and command signals between flash memorychips 670, 672 and the memory I/O unit 652. Flash bus 675 includes 16bit lines, 8 bit lines of which form a first bus 680 connected to a port682 of I/O register 671 of the first flash memory chip, and another 8bit lines of which form a second bus 684 connected to a port 686 of I/Oregister 673 of the second flash memory chip.

Memory bus 512 also includes: a control bus 690 which connects a controlsignal (CTRL signal) output 692 of the flash state machine 642 to aninput 694 of the first flash memory chip and to an input 696 of thesecond flash memory chip; a chip enable line 698 which connects a chipenable (CE) output 700 of the flash state machine 642 to an enable input702 of the first flash memory chip and to enable an input 704 of thesecond flash memory chip; and a ready/busy signal (FRDY-BSY* signal)line 706 which connects an output 708 of the first flash memory chip andan output 710 of the second flash memory chip roll to an input 712 ofthe flash state machine 642.

Microprocessor 620, at times (for example, during initialization of thememory system), executes program instructions (or code) stored in ROM632, and at other times, such as during operation of the memory system,the microprocessor executes code that is stored in code storage unit626, which may be either a volatile, i.e., read-and-write memory (RAM)or a non-volatile, i.e., EEPROM, type of memory storage. Prior to theexecution of program code from code storage unit 626, the program codemay be stored in the memory bank 506 and later downloaded to the codestorage unit for execution thereof. During initialization, themicroprocessor 620 can execute instructions from ROM 632.

Sector-organized information, including user data and overheadinformation, is received at host interface 610 from host 504 via hostbus 514 and provided to the data buffer 614 for temporary storagetherein. Sectors of information stored in the data buffer are retrievedunder control of flash state machine 642 and provided to memory bank 506in a manner further described below. It is common in the industry foreach sector to include 512 bytes of user data plus overhead information.Although a sector may include other numbers of bytes of information, inthe preferred embodiment, a sector has 512 bytes of user data and 16bytes of overhead information.

ECC logic block 660 includes circuitry for performing error coding andcorrection on the sector-organized information. ECC logic block 660performs error detection and/or correction operations on the user dataportions of each sector stored in the flash memory chips 670, 672 ordata received from host 504.

When required, the space manager 636 finds a next unused (or free)non-volatile memory location within the memory bank for storing a blockof information with each block including multiple sectors ofinformation. In the preferred embodiment, a block includes 32 sectorsalthough, alternatively a block may be defined to include another numberof sectors such as, for example, 16. The physical address of a storageblock located within memory bank 506, referred to as a virtual physicalblock address (virtual PBA), and the physical block address of a sectorof information located within the memory bank 506, referred to as anactual physical block address (actual PBA), is determined by the spacemanager by performing a translation of a logical block address (LBA)received from the host. An actual LBA received from host 504 (ahost-provided LBA) identifies a sector of information. Space manager 636includes a space manager memory unit, which is preferably a volatilememory unit, for storing an LBA-PBA map for translating a modifiedversion of the host-provided LBAs to virtual PBAs as further explainedbelow. In the depicted embodiment, the space manager includes a spacemanager RAM unit (SPM RAM unit) 720 for storing the LBA-PBA map underthe control of a space manager controller (SPM controller) 724 which iscoupled to the SPM RAM unit.

FIG. 7 shows a table diagram generally illustrating organization of userdata, error correction information, and flag information stored inmemory bank 506 in accordance with an embodiment of the presentinvention. Memory bank 506 includes a plurality of M blocks 727designated BLCK0, BLCK1, BLCK(M-1), each having a virtual physical blockaddresses (PBA). Each of the blocks 727 includes a plurality of N memoryrow locations 728 designated ROW0, ROW1, . . . ROW15 where, in thepreferred embodiment, N=16. Each block 727 of memory bank 506 iscomprised of a first sub-block 730 of first flash memory chip 670, and acorresponding second sub-block 731 of second flash memory chip 672.Corresponding sub-blocks 730, 731, which together form a block, areidentified by the same virtual PBA. Each memory row location 728includes a first row-portion 732 and a corresponding second row-portion733 In the depicted embodiment each of the first and second row-portions732, 733 includes storage for 512 bytes of data information plusadditional storage space for other information. In the depictedembodiment, the storage of information in the first row-portions 732 ofthe first flash memory chip is accomplished in a manner dissimilar fromthat in the second row-portions 733 of the second flash memory chip.

Each of the first row-portions 732 includes: a first even sector field734 for storing even data bytes D0, D2, D4, . . . D510 of an even sector(S0, S2, S4, . . . ) of information; a first spare field 736; a firstodd sector field 738 for storing even data bytes D0, D2, D4, . . . D510of an odd sector (S1, S3, S5, . . . ) of data; and a second spare field740. Each of the second row-portions 733 includes: a second even sectorfield 742 for storing odd data bytes D1, D3, D5, . . . D511 of the evensector of data which has it's corresponding even data bytes stored infirst even sector field 734; a first error correction field 744 forstoring error correction information corresponding to the even sector ofinformation stored collectively in fields 734 and 742; a second oddsector field 746 for storing odd data bytes of the odd sector ofinformation which has it's even data bytes stored in first odd sectorfield 738; a second error correction field 748 for storing ECCinformation corresponding to the odd sector of information storedcollectively in fields 738 and 746; a block address field 750; and aflag field 752. Fields 734 and 742 form an even sector location whilefields 738 and 746 form an odd sector location. It is understood in thepresent invention that fields 734 and 742 could alternatively form anodd sector location while fields 738 and 746 could alternatively form aneven sector location, and that fields 734 and 738 could alternatively beused to store odd data bytes while fields 742 and 746 couldalternatively be used to store even data bytes. Additionally, firstrow-portion 732 could alternatively be used for storing the overheadinformation relating to the sectors stored in the memory row location728.

Flag field 752 is used for storing flag information which is used bycontroller 510 (FIG. 6) during access operations as further explainedbelow. Block address field 750 is used for storing a modified version ofa host-provided LBA value which is assigned to a block, as furtherdescribed below. Only a single block address entry is required in theblock address field per block. In a preferred embodiment, a modifiedhost-provided LBA value is entered in block address field 759 of the Nthrow, ROW15, of the row locations 728 of each block 727.

In operation, the controller 510 (FIG. 6) accesses an even sector ofinformation stored collectively in the first and second flash memorychips by simultaneously accessing first and second even sector fields734, 742 of corresponding row-portions of the first and second flashmemory chips via the first and second split buses 680, 684 (FIG. 6),respectively. The first and second split buses 680, 684 (FIG. 6) includelines coupled to receive the even and odd data bytes respectively of asector of information. The controller 510 (FIG. 6) accesses an oddsector of information stored collectively in the first and second flashmemory chips by simultaneously accessing the first and second odd sectorfields 738, 746 via the first and second split buses 680, 684 (FIG. 6),respectively. The split buses 680, 684 (FIG. 6) also provide for:transmission of ECC information between the flash memory chips and theflash state machine 642 and ECC logic unit 660 of the memory controller510; and transmission of address information from flash state machine642 to the flash memory chips.

Controller 510 (FIG. 6) monitors the status of blocks 727 of memory bank506 using the space manager 636. In one embodiment, controller 510 (FIG.6) monitors the status of each block location 727 of the memory bankusing block level flags including a used/free block flag and a defectblock flag stored in a used flag location 754 and a defect flag location756 respectively of the flag field 752. Block level flags provideinformation concerning the status of a whole block 727 of the memorybank and therefore, only a single block level flag entry is required inthe flag locations 754 and 756 per block. The used/new block flagindicates whether the corresponding block 727 is currently being “used”to store information or whether it is available (or free) to storeinformation. The defect block flag indicates whether the correspondingblock 727 is defective.

In another embodiment, controller 510 (FIG. 6) monitors the status ofeach memory row location 728 of the memory bank using flags including aused/free row flag stored in the used flag location 754, a defect rowflag stored in the defect flag location 756, an old row flag stored inan old flag location 758 of the flag field 752, an even sector move flagstored in an even sector move flag location 760, and an odd sector moveflag stored in an odd sector move flag location 762. In this embodiment,the used/new flag indicates whether the corresponding memory rowlocation 728 is currently being “used” to store information or whetherit is available (or free) to store information. The defect flagindicates whether the memory block 727 is defective. If either of acorresponding pair of non-volatile memory locations 732, 733 isdetermined to be defective, then the whole memory block 727 is declaredto be defective as indicated by the value in the defect flag location756 being set, and the defective block can no longer be used. In apreferred embodiment, locations 758, 754, and 756 are included in asingle 3-bit flag location 764.

The even and odd sector move flag locations 760, 762 store valuesindicating whether the corresponding even and odd sectors stored in thenon-volatile memory sector location have been moved to another locationwithin the non-volatile memory bank 506 (FIG. 6). For example, if aneven sector of information stored collectively in a particular pair ofeven sector fields 734, 742 of a row location 728 has been moved toanother pair of even sector fields in the non-volatile memory bank 506,the value in the corresponding even sector move flag location 760 isset. Similarly, if an odd sector of information stored collectively inthe odd sector fields 738, 746 of the same row location has been movedto another pair of odd sector fields in the non-volatile memory bank,then the value in the corresponding odd sector move flag location 672 isset. The location within the non-volatile memory bank 506 to which asector of information has been moved is indicated in the LBA-PBA mapstored in the SPM RAM 720 in an MVPBA address location, as taught in apatent application, filed by the inventors of this application, entitled“Moving Sectors Within a Block of Information In a Flash Memory MassStorage Architecture”, Ser. No. 08/831,266, filed Mar. 31, 1997, thedisclosure of which is incorporated herein by reference. In a preferredembodiment, locations 760 and 762 are formed by a single 2-bit move-flaglocation 766.

FIG. 8A shows a table diagram generally illustrating organization of anexemplary LBA-PBA map at 800, which is stored in SPM RAM 720 (FIG. 6),for translating a modified version of the host-provided LBA's to PBA's.The modified host-provided LBA is derived by dividing the host-providedLBA by the number of sectors with a block, as explained in more detailbelow. The depicted LBA-PBA map includes: a plurality of map rowlocations 802 which are addressable by a modified host-provided LBA orby a virtual PBA; a virtual PBA field 804 for storing a virtual PBAvalue identifying a block 727 (FIG. 7) within the memory bank; and aflag field 806 for storing flag information. As previously mentioned,the actual PBA specifies the location of a sector of information in thememory bank and the virtual PBA specifies the location of a block 727(FIG. 7) in the memory bank. Virtual PBA values are retrieved by spacemanager 636 (FIG. 7) from the depicted map and transferred to port 648of the flash state machine 642 for use in addressing blocks withinmemory bank 506.

FIG. 8B shows a block diagram illustrating a host-provided-LBA format810 and an actual PBA format 820. LBA format 810 includes “offset bits”812, which comprise the least significant bits of the host-provided LBAvalue. As explained above, in the preferred embodiment, each block 727(FIG. 7) includes memory space for storing 32 sectors of information,each sector includes 512 bytes of user data and 16 bytes of overheadinformation. Because each block 727 (FIG. 7) includes 32 sectors in thepreferred embodiment, five offset bits 812 are required to identify eachof the 32 sectors in each block. In this embodiment; the translation ofthe host-provided-LBA to actual and virtual PBA values is performed byfirst masking the five least significant “offset” bits 812, of thehost-provided-LBA, shifting the result to the right by 5 bits and usingthe shifted value as a modified host-provided LBA value or an“LBA-map-value” to address a map row location 802 in the LBA-PBA map 800(FIG. 8A). This, in effect, is dividing the host-provided LBA by 32. Theactual PBA value 820, which specifies the location of a sector within ablock of the memory bank, is formed by concatenating offset bits 812 ofthe LBA value with a virtual PBA 822 value stored in the correspondingfield 804 (FIG. 8A) of the LBA-PBA map. That is, the virtual PBA value822 is used to identify a block within the memory bank and the fiveremaining offset bits 812 are used to address a sector within theidentified block.

Upon initialization of memory system 600 (FIG. 6), the virtual PBA valuestored in the virtual PBA field 804 of each map row location 802 is setto an all ‘1’s state. Each time a block 727 (FIG. 7) is accessed by thecontroller, such as during a write operation, the virtual PBA valuestored in the corresponding virtual PBA field 804 of the correspondingmap row location is modified by the space manager controller 724 (FIG.6) to specify a new virtual PBA value. When a block within the memorybank 506 is erased, the old virtual PBA value (the virtual PBA valuecorresponding to the erased block), rather than a modified version ofthe host-provided LBA, is used to address the SPM RAM 720 (FIG. 6) andthe used flag, stored within the flag field of the SPM RAM 720, iscleared. This same ‘used’ flag within the flag field of the SPM RAM 720is set at the time when the corresponding virtual PBA is updatedpointing to the new block in the memory bank where sector information ismaintained (step 1214).

FIG. 9 shows a timing diagram illustrating the timing of control,address, and data signals for a write operation performed by memorysystem 600 (FIG. 6) wherein two sectors of information aresimultaneously written in the non-volatile memory bank 506 (FIG. 6)during a single write operation. The diagram includes: a wave form 902representing a first flash signal which transmits time multiplexedcommand, address, and data information from flash state machine 642(FIG. 6) of the controller via bus 680 (FIG. 6) to port 682 of the firstflash memory chip; a wave form 904 representing a second flash signalwhich transmits time multiplexed command, address, and data signals fromthe flash state machine via bus 684 (FIG. 6) to port 686 of the secondflash memory chip; a time line 905; and a plurality of control signalwave forms.

The control signal wave forms include: a wave form 906 representing acommand line enable signal (CLE signal) transmitted from flash statemachine 642 (FIG. 6) to the first and second flash memory chips viacontrol bus 690 (FIG. 6); a wave form 908 representing an address lineenable signal (ALE signal) transmitted from the flash state machine tothe flash memory chips via the control bus; a wave form 910 representinga write enable signal (WE signal) transmitted from the flash statemachine to the flash memory chips via the control bus; a wave form 912representing a read enable signal (RE signal) transmitted from the flashstate machine to the memory chips via the control bus; a wave form 914representing a flash chip enable signal (FCE* signal) transmitted fromchip enable signal output 700 (FIG. 6) of the flash state machine viachip enable line 698 to the first and second flash memory chips; a waveform 916 representing a flash ready/busy signal (FRDY_BSY* signal)transmitted from outputs 708 and 710 (FIG. 6) of the first and secondflash memory chips to the flash state machine via flash ready/busysignal line 706.

The write operation commences at a time t0 at which the FCE* signal(wave form 914) transitions from a HIGH state to a LOW state therebyenabling the first and second flash memory chips to begin receivingcommand, address, data, and control signals. Prior to time to, theFRDY_BSY* signal (wave form 916), transmitted from the flash memorychips to input 712 of the flash state machine (FIG. 6), is alreadyactivated indicating that the first and second flash memory chips areready to receive access commands. At a subsequent time t1, the CLEsignal (wave form 906) is activated, transitioning from a LOW state to aHIGH state, thereby enabling the first and second flash memory chips toread command signals. At a time t2, the first and second flash signals(wave forms 902 and 904) simultaneously transmit a serial data shift-incommand signal 80H to the first and second flash memory chips via thefirst and second first split buses 680 and 684 respectively. At a timet3, while the serial data shift-in command signals 80H are active, theWE signal (wave form 910) transitions from a HIGH state to a LOW statethereby enabling the first and second flash memory chips to read theserial data command signals 80H. At a time t4, the CLE signal (wave form906) is deactivated, transitioning back to the LOW state, therebydisabling the flash memory chips from reading command signals.

Also at time t4, the ALE signal (wave form 908) is activated,transitioning from a LOW state to a HIGH state, thereby enabling thefirst and second flash memory chips to read packets of addressinformation. At times t5, t6, and t7, the first and second flash signals(wave forms 902 and 904) each transmit first, second, and third addresspackets ADD0, ADD1, and ADD2 respectively to the first and second flashmemory chips. At a time t8, the ALE signal (wave form 908) isdeactivated, transitioning from the HIGH state to a LOW state, therebydisabling the first and second flash memory chips from reading addressinformation. During time intervals between times t5 and t6, t6 and t7,and t7 and t8, the WE signal (wave form 910) transitions from a HIGHstate to a LOW state thereby enabling the first and second flash memorychips to read the read the first, second, and third address packetsADD0, ADD1, and ADD2 respectively. The three address packets ADD0, ADD1,and ADD2 specify a row-portion 732, 733 within a first sub-block 730(FIG. 16).

At a time t9, the first and second flash signals (wave forms 902 and904) begin simultaneously transmitting interleaved even and odd databytes wherein the even and odd bytes form one sector of information. Theeven bytes are transmitted to the first flash memory chip via bus 680(FIG. 6) and the odd sector bytes are transmitted to the second flashmemory chip via bus 684 (FIG. 6). The even data bytes D0, D2, D4, . . .D510 of the even sector are received by the first flash chip and storedin the first even sector field 734 (FIG. 16) of the correspondinglocation 732 of the first flash memory chip. This is done by storing abyte each time the write enable signal WE* (Wave form 910) is activated.The odd data bytes D1, D3, D5, . . . D511 of the even sector arereceived by the second flash chip and stored in the second even sectorfield 742 (FIG. 16) of the corresponding location 733 thereof with eachbyte being stored when the WE* signal is activated. At a time t10, thefirst and second flash signals (wave forms 902 and 904) completetransmission of the interleaved even and odd data bytes of the evensector.

Immediately after time t10, during an interval between time t10 and atime t11, the first flash signal (wave form 902) transmits four packetsof filler information (FFH, hexadecimal F, equivalent binary value“1111,” decimal value “15”) to the first flash memory chip via the firstsplit bus 680 (FIG. 6) while the second flash signal (wave form 904)transmits error correction codes (ECC) to the second flash memory chipvia the second split bus 684 (FIG. 6). The filler information FFHtransmitted during this time period is received by the first flashmemory chip and stored in the first spare field 736 (FIG. 16). The errorcorrection code transmitted during this time period is received by thesecond flash memory chip and stored in the first error correction field744 (FIG. 16) of the nonvolatile memory section 733 of the second flashmemory chip. This error correction code, generated by ECC logic unit 660(FIG. 16), relates to the even sector transmitted during the precedingtime interval between time t10 and t11.

At a time t11, the first and second flash signals (wave forms 902 and904) begin simultaneously transmitting interleaved even and odd databytes, synchronous with the write enable signal WE* (wave form 910), ofan odd sector to the first and second flash memory chips via the firstand second first split buses 680 and 684 (FIG. 6) respectively. The evendata bytes D0, D2, D4, . . . D510 of the odd sector are received by thefirst flash chip and stored to the first odd sector field 738 (FIG. 16)of the corresponding location 732 of the first flash memory chip. Theodd data bytes D1, D3, D5, . . . D511 of the odd sector are received bythe second flash memory chip and stored to the second odd sector field746 (FIG. 16) of the corresponding location 733 of the second flashmemory chip. At a time t12, the first and second flash signals (waveforms 902 and 904) complete transmission of the interleaved even and odddata bytes of the odd sector.

Immediately after time t12, during an interval between time t12 and atime t13, the first flash signal (wave form 902) transmits noinformation to the first flash memory chip thereby maintaining the valuein corresponding storage location bytes of the first flash memory chipat FFH (hexadecimal) or all 1's in binary. Meanwhile, between time t12and time t13, while the second flash signal (wave form 904) transmitserror correction codes (ECC) to the second flash memory chip via thesecond split bus 684 (FIG. 6). The filler information FFH transmittedduring this time period is received by the first flash memory chip andstored to the second spare field 740 (FIG. 16). The error correctioncode transmitted during this time period is received by the second flashmemory chip and stored to the second error correction field 748 (FIG.16) of the nonvolatile memory section 733 of the second flash memorychip. This error correction code, generated by ECC logic unit 660 (FIG.16), relates to the odd sector transmitted during the preceding timeinterval between time t11 and t12.

At a time t17, the first and second flash signals (wave forms 902 and904) each transmit a read command signal 70H to the first and secondfirst and second flash memory chips via the first and second split buses680 and 684 respectively. While the read command signals 70H are active,the WE signal (wave form 910) transitions from a HIGH state to a LOWstate thereby enabling the first and second flash memory chips to readthe read command signals 70H. At a time t18, the CLE signal (wave form906) is deactivated, transitioning back to the LOW state, therebydisabling the flash memory chips from reading command signals.

At a time t18, the first and second flash signals (wave forms 902 and904) each transmit a status command signal STATUS to the first andsecond first and second flash memory chips via the first and secondsplit buses 680 and 684 respectively. While the read command signals 70Hare active, the WE signal (wave form 910) transitions from a HIGH stateto a LOW state thereby enabling the first and second flash memory chipsto read the read command signals 70H.

FIG. 10 shows a table diagram generally illustrating the memory storageformat, as depicted in FIG. 7, for storing a block of information inmemory bank 506 (FIG. 6) wherein a single sector is written to aparticular memory row location of the memory bank. As shown, a memoryrow location 728 designated ROW1 has an even sector S2 and an odd sectorS3 stored therein in accordance with the format described above inreference to FIG. 7. A memory row location 728 designated ROW2 has asingle even sector S4 stored in the first and second even sector fields734 and 742 of a corresponding pair of row-portions of the first andsecond flash memory chips 670, 672. Because no odd sector is required tobe stored in this case, fields 736, 738, 746, 748, 750, and 752 areshown to be erased.

FIG. 11 shows a table diagram illustrating the alternative memorystorage format, as depicted in FIG. 7, for storing a block ofinformation in memory bank 506 (FIG. 6) wherein a single sector iswritten to a particular memory row location of the memory bank. Asmentioned above, field 764 is a three bit field which is used forstoring the old row flag in the first bit place, the used/free row flagin the second bit place, and the defect row flag in the third bit place.Also as described above, field 766 is a two bit field which is used forstoring 1the even sector move flag in the first bit place and the oddsector move flag in the second bit place.

The memory row location designated ROW1, having sectors S2 and S4 storedtherein, has a value “00” stored in field 766 indicating that bothsectors have been moved elsewhere in the memory bank. The memory rowlocation designated ROW2, having a single even sector S4 stored in thefirst and second even sector fields 734 and 742, has a value “01” storedin field 766 indicating that the information in S4 has been updated andnow resides elsewhere in the memory bank. A value of logic state “0”generally indicates that moved sectors have been updated by the host.Therefore, when the remaining sectors are moved from the old block whichwas not updated by the host, it can be determined that these sectors arenot to be overwritten by the old data during the move.

A memory location 728 designated ROW1 has an even sector S2 and an oddsector S3 stored therein in accordance with the format described abovein reference to FIG. 7. A memory location 728 designated ROW2 has asingle even sector S4 stored in the first and second even sector fields734 and 742 of a corresponding pair of row-portions of the first andsecond flash memory chips 670, 672. Because no odd sector is required tobe stored in this case, fields 736, 738, 746, 748, 750, and 752 areshown to be erased.

FIG. 12 is a flowchart illustrating a process of simultaneously writingtwo sectors of information to two memory units during a single writeoperation in accordance with the present invention. In step 1202, thememory controller 510 (FIG. 6) receives host addressing information fromhost 504 which specifies addresses for one or more sector locations, inthe form of a logical block address (host-provided LBA) or in the formof cylinder head sector (CHS) information. If the host addressinginformation is in the form of CHS information, the controller translatesthe CHS information to LBA information. As mentioned, the sectors areorganized in blocks and therefore, the host-provided LBA's maycorrespond to sectors of more than one block. This information is usedby microprocessor 620 (FIG. 6) as will be further discussed below.

Microprocessor 620 (FIG. 6) executes instructions, which are stored incode storage unit 626 (FIG. 6) to carry out the depicted process. Instep 1204, a sector count value is set equal to the number of sectorlocations of a current block, being addressed by the host wherein asector location may, for example, be comprised of fields 734 and 742(FIG. 7) or fields 738 and 746 (FIG. 7) of the memory bank. Themicroprocessor determines at 1206 whether or not each of the sectorlocations specified by the host-provided LBA values has been accessed bythe host before. This determination is made by reading the contents ofthe corresponding virtual PBA field 804 (FIG. 8A) of the LBA-PBA map 800stored in SPM RAM 720 (FIG. 6). As explained above in reference to FIG.8A, if the virtual PBA value corresponding to a host-provided LBA is setto the all ‘1’s state, then the corresponding LBA was not accessed bythe host before. Memory space in memory bank 506 is erased a block at atime. If any sectors of a block have been accessed since a last erasureof the block, then the block is indicated as having been accessed byvirtue of the virtual PBA value in field 804 (FIG. 8A) of thecorresponding map row location of the LBA-PBA map being a value otherthan “all 1's”.

If it is determined that one or more sector locations, of the currentblock, specified by the host-provided-LBA's have been accessedpreviously by the host, the write process proceeds to step 1210 in whichmicroprocessor 620 (FIG. 6) sets the corresponding one of the move flags760, 762 (FIG. 7) corresponding to the current sector location, and thewrite process proceeds to step 1208. As earlier discussed, maintainingthe ‘move’ flag in non-volatile memory is optional and may be entirelyeliminated without departing from the scope and spirit of the presentinvention. In the absence of move flags, the microprocessor maintainsthe status of sectors as to whether or not they have been moved to otherblocks. This is done by keeping track of two values for each block. Onevalue is the starting sector location within a block where sectors havebeen moved and the second value is the number sectors within the blockthat have been moved. With these two values, status information as towhether or not and which sectors of a block have been moved to otherblock(s) may be reconstructed.

If it is determined, at step 1206, that none of the sector locations ofthe current block specified by the host-provided-LBA have beenpreviously accessed, the write process proceeds directly to step 1208.

In step 1208, the space manager 636 (FIG. 6) of the controller searchesfor a free (or unused) block, such as block 727 (FIG. 7) located withinthe nonvolatile memory bank, each free block being identified by aspecific virtual PBA value. The microprocessor determines at 1212whether a free block is located, and if not, an error is reported by thecontroller 510 (FIG. 6) to the host indicating that the nonvolatilememory bank is unable to accommodate further storage of information. Asthis can result in a fatal system error, the inventors of the present1invention have exercised great care in preventing this situation fromoccurring.

Once a free block within the nonvolatile memory is located at step 1208,the depicted process proceeds to step 1214. In step 1214, microprocessor620 prompts space manager 636 (FIG. 6) to assign a virtual PBA value 822(FIG. 8B) to the free block found in step 1208. This virtual PBA valueis stored in the LBA-PBA map 800 (FIG. 8A) in a map row location 802(FIG. 8A) identified by the masked bits 814 (FIG. 8B) of thehost-provided LBA corresponding to the current block. The masked bits814 (FIG. 8B) of the current host-provided LBA are obtained by shiftingthe host-provided LBA to the right by the 5 offset bits (or by dividingby 32). For example, if the host-identified LBA is 16H (hexadecimalnotation), the row in which the virtual PBA is stored is row 0. Also atstep 1214, the microprocessor appends the ‘offset’ bits 812 (FIG. 8B) tothe virtual PBA corresponding to the found free block to obtain anactual PBA value 820 (FIG. 8B). At 1216, the microprocessor determineswhether the actual PBA value is an even or odd value. At 1216,alternatively, the host-provided LBA may be checked in place of theactual PBA value to determine whether this value is odd or even.

If it is determined at 1216 that the actual PBA value is even, theprocess proceeds to 1218 at which the microprocessor determines whetherthe sector count is greater than one, i.e., there is more than onesector of information to be written at the point the controller requeststhat more than one sector to be transferred from the host to theinternal buffer of the controller and the process proceeds to 1232 atwhich the microprocessor determines whether two sectors of informationhave been transferred from the host to the data buffer 614 (FIG. 6)(through the host interface circuit 610). That is, where there is morethan one sector of information that needs to be written to nonvolatilememory, as detected by the flash state machine 642, two sectors ofinformation are transferred at-a-time from the host to the data buffer614. The data buffer 614 is used to temporarily store the sectors'information until the same is stored into the memory bank 506. In thepreferred embodiment, each sector includes 512 bytes of user data and 16bytes of overhead information.

Where two sectors of information have not yet been transferred to thedata buffer 614, the microprocessor waits until such a transfer iscompleted, as shown by the ‘NO’ branch loop at 1232.

At step 1234, the microprocessor initiates the writing of the twosectors that have been temporarily saved to the data buffer to thememory bank 506 (FIG. 6) by issuing a write command, followed by addressand data information. The write operation at step 1234 is performedaccording to the method and apparatus discussed above relative to FIGS.7 and 9.

Upon completion of writing two sectors of information, the writeoperation is verified at 1235. If information was not correctlyprogrammed into the sectors at step 1234, the process continues to step1237 where a defect management routine is performed, as will bediscussed in greater detail below. After execution of the defectmanagement routine, the sector count is decremented by two at step 1236.At 1235, if the write operation was verified as being successful, step1236 is executed and no defect management is necessary. Themicroprocessor then determines at 1238 whether the sector count is equalto zero and if so, it is assumed that no more sectors remain to bewritten and the process proceeds to 1228. If, however, more sectors needto be written the process proceeds to step 1240 at which thehost-provided LBA is incremented by two to point to the next sector thatis to be written.

At step 1240, the microprocessor determines whether the last sector ofthe block has been reached. The block boundary is determined bycomparing the ‘offset’ value of the current LBA to the number of sectorsin a block, and if those values are equal, a block boundary is reached.For example, in the preferred embodiment, since a block includes 32sectors, the ‘offset’ value of the current LBA is compared against ‘32’(in decimal notation). If alternatively, a block is defined to haveother than 32 sectors, such as 16 sectors, the latter is comparedagainst the ‘offset’. If a block boundary in the nonvolatile memory isreached, the write process continues from step 1206 where the virtualPBA value corresponding to the current LBA value is checked for an all‘1’s condition and so on. If a block boundary is not reached at step1242, the write process continues from step 1218.

At step 1218, if it is determined that the sector count is not greaterthan one, the microprocessor proceeds to determine at 1220 whether databuffer 614 (FIG. 6) has received at least one sector of information fromthe host. If not, the microprocessor waits until one sector ofinformation is transferred from the host to the data buffer 614. Uponreceipt of one sector of information, writing of the next sector isinitiated and performed at step 1222 according to the method andapparatus discussed above relative to FIGS. 10 and 11. Upon completionof writing a sector of information, the write operation is verified at1223. If information was not correctly programmed into the sector atstep 1222, the process continues to step 1225 where a defect managementroutine is performed, as will be discussed in greater detail below.After execution of the defect management routine, at step 1224, thesector count is decremented by one. If at 1223, it is determined thatthe write operation was correctly performed, the process continues tostep 1224 and no defect management routine is executed. At 1226, themicroprocessor determines whether the sector count is equal to zero and,if not, the host-provided LBA is incremented by one and the writeprocess continues to step 1242 where the microprocessor checks for ablock boundary as explained above.

If at step 1226, as in step 1238, it is determined that no more sectorsremain to be written, i.e. the sector count is zero, the depictedprocess proceeds to 1228 at which the microprocessor determines whetherthe move flag is set. As noted above, the move flag would be set at step1210 if it was determined at 1206 that an LBA was being re-accessed bythe host.

If it is determined at 1228 that the move flag is not set, the writeprocess ends. However, upon a determined at 1228 that the move flag isset, the block is updated. That is, those sectors of the current blockthat were not accessed are moved to corresponding sector locations inthe block within memory bank 506 identified by the virtual PBA valueassigned in step 1214 to the free block found in step 1208. This isperhaps best understood by an example.

Let us assume for the purpose of discussion that the sectors identifiedby LBAs 1, 2, 3, 4, 5 and 6 have already been written and that the hostnow commands the controller to write data to sectors identified by LBAs3, 4 and 5. Further, let us assume that during the first write processwhen LBAs 1-6 were written, they were stored in a block location in thememory bank 506 (FIG. 6) identified by a virtual PBA value of “3” andthe LBA locations 3, 4 and 5 are now (during the second write process)being written to a location in the memory bank identified by a virtualPBA value of “8”. During writing of locations identified byhost-provided LBA values of 3, 4, and 5, the microprocessor at step 1206determines that these block locations are being re-accessed and the moveflag at 1210 is set. Furthermore, at step 1230, after the sectors,identified by host-provided LBAs 3, 4, and 5, have been written tocorresponding sectors of the block identified by virtual PBA “8”,sectors in the block identified by virtual PBA “3” that were notre-accessed during the write operation are moved from the blockidentified by virtual PBA “3” to corresponding sector locations of theblock identified by virtual PBA “8” and the block identified by virtualPBA “3” is thereafter erased. This example assumes that remainingsectors of the block identified by virtual PBA “3”, such as sectors 0and 7-31 (assuming there are 32 sectors in a block), were not accessedsince the last erase of the block in which they reside and thereforecontain no valid sector information. Otherwise, if those sectors werepreviously accessed, then they would also be moved to the virtual PBAlocation 8.

Step 1230 may be implemented in many ways. The inventors of the presentinvention disclose various methods and apparatus which may bealternatively employed for performing the move operation of step 1230.In patent applications, Ser. No. 08/946,331 entitled “Moving SequentialSectors Within a Block of Information In a Flash Memory Mass StorageArchitecture”, filed on Oct. 7, 1997, and Ser. No. 08/831,266 entitled“Moving Sectors Within a Block of Information In a Flash Memory MassStorage Architecture”, filed on Mar. 31, 1997, the disclosures of whichare herein incorporated by reference.

FIG. 12a shows the steps performed by the microprocessor if the defectmanagement routine at steps 1237 and 1225 (in FIG. 12) is executed. Theblock management routine is executed when the write operation is notsuccessfully verified; the block(s) being programmed is in some waydefective and a different area in the nonvolatile memory, i.e. anotherblock need be located for programming therein.

At step 1600, the block that was being unsuccessfully programmed ismarked as “defective” by setting the “defect” flags 756 (in FIG. 7). Atstep 1602, the space manager within the controller is commanded to finda free block. At step 1604, the information that would have beenprogrammed at steps 1234 and 1222 (in FIG. 12) i.e. the block marked“defective” is programmed into corresponding sector locations within thefree block found in step 1602.

At step 1606, the block marked “defective” is checked for the presenceof any sector information that was previously written theretosuccessfully. If any such sectors exist, at step 27. 1608, thesepreviously-programmed sectors are moved to the free block, as isadditional block information in the process of FIG. 12.

FIG. 13 shows a table diagram generally illustrating a memory storageformat for storing a block, including 32 sectors, of information inmemory bank 506 in accordance with an alternative embodiment of thepresent invention. In this embodiment, an even sector is stored in afirst row portion located in a first of the two memory units and an oddsector is stored in a second row portion located in the second of thetwo memory units. In the depicted embodiment, memory bank 506 includes aplurality of M blocks 1302 designated BLCK0, BLCK1, BLCK(M-1) eachhaving a physical block addresses (PBA). Each of the blocks 1302includes a plurality of N memory row locations 1304, and in a preferredembodiment, N=16. Each block 1302 of memory bank 506 is comprised of afirst sub-block 1306 of first flash memory chip 670, and a correspondingsecond sub-block 1308 of second flash memory chip 672 wherein thecorresponding sub-blocks are identified by the same virtual PBA. Eachmemory row location 1304 includes a first row-portion 1310 and acorresponding second row-portion 1312. In the depicted embodiment eachof the first and second row-portions 1310, 1312 includes storage for 512bytes of data information plus additional storage space for errorcorrection information (ECC information) and flag information.

Each of the first row-portions 1310 includes an even sector field 1314for storing an even sector (S0, S2, S4, . . . ) of information, and aneven sector error correction field 1316 for storing error correctioninformation corresponding to the even sector stored in field 1314. Eachof the second row-portions 1312 includes an odd sector field 1318 forstoring an odd sector (S1, S3, S5, . . . ) of information, an odd sectorerror correction field 1320 for storing error correction informationcorresponding to the odd sector stored in 1318, a block address field1322, and a flag field 1324. It is understood in the present inventionthat field 1314 could alternatively be used to store an odd sector whilefield 1318 could alternatively be used to store an even sector. Also,first row-portion 1310 could alternatively be used for storing the blockaddress and flags.

Flag field 1324 is used for storing flag information which is used bycontroller 510 (FIG. 6) during access operations as further explainedbelow. Block address field 1322 is used for storing the block addresspermanently assigned to block 1302, such as “0” for BLCK0. Only a singleblock address entry is required in the block address field per block. Ina preferred embodiment, a block address entry is entered in blockaddress field 1322 of the last row 1304, which is row 15.

In this alternative embodiment, the first and second split buses 680,684 (FIG. 6) include lines coupled to receive data bytes of the even andodd sectors respectively. The controller 510 (FIG. 6) writes two sectorssimultaneously by simultaneously writing a byte of an even sector and anodd sector simultaneously via the first and second split buses 680, 684(FIG. 6), respectively. The split buses 680, 684 (FIG. 6) also providefor: transmission of ECC information between the flash memory chips andthe flash state machine 642 and ECC logic unit 660 of the memorycontroller 510; and transmission of address information from flash statemachine 642 to the flash memory chips.

FIG. 14 shows a timing diagram illustrating the timing of controlsignals, address signals, and data signals for an erase operation of thememory system of FIG. 6. The diagram includes: the wave form 902representing the first flash signal which transmits time multiplexedcommand, address, and data information from the flash state machine 642(FIG. 6) via first split bus 680 (FIG. 6) to the first flash memorychip; the wave form 904 representing the second flash signal whichtransmits time multiplexed command, address, and data signalstransmitted from the flash state machine via second split bus 684 (FIG.6) to the second flash memory chip; a time line 1450; and a plurality ofcontrol signal wave forms. The control signal wave forms, all of whichare described above, include: wave form 906 representing the commandline enable (CLE) signal; wave form 908 representing the address lineenable (ALE) signal; wave form 910 representing the write enable (WE)signal; wave form 912 representing the read enable (RE) signal; waveform 914 representing the flash chip enable (FCE*) signal; and wave form916 representing the flash ready/busy signal (FRDY_BSY* signal).

The erase operation commences at a time E0 at which the FCE* signal(wave form 914) transitions from a HIGH state to a LOW state therebyenabling the first and second flash memory chips to begin receivingcommand, address, and data signals. At a subsequent time E1, the CLEsignal (wave form 906) is activated, transitioning from a LOW state to aHIGH state, thereby enabling the first and second flash memory chips toread command signals. At a time E2, the first and second flash signals(wave forms 902 and 904) each transmit a command signal. The first flashsignal (wave form 902) transmits an ‘erase set’ command, 60H, via thefirst split bus 680 (FIG. 6) to the first flash memory chip while thesecond flash signal (wave form 904) transmits a read status commandsignal 70H via the second split bus 684 (FIG. 6) to the second flashmemory chip. At a time E3, while the command signals 60H and 70H areactive, the WE signal (wave form 910) transitions from a HIGH state to aLOW state thereby enabling the first and second flash memory chips toread the command signals 60H and 70H. At a time E4, the CLE signal (waveform 906) is deactivated, transitioning back to the LOW state, therebydisabling the flash memory chips from reading command signals.

Also at time E4, the ALE signal (wave form 908) is activated,transitioning from a LOW state to a HIGH state, thereby enabling thefirst and second flash memory chips to read packets of addressinformation. At times E5 and E6, the first flash signal (wave form 902)transmits first and second address packets ADD0 and ADD1 respectively tothe first flash memory chip wherein the first and second address packetsADD0 and ADD1 specify a sub-block 730 (FIG. 7) of the first flash memorychip 670 of the memory bank. At a time E7, the ALE signal (wave form908) is deactivated. During time intervals between times E3 and E4, andE4 and E5, the WE signal (wave form 910) transitions to the LOW state toenable the flash memory chip to read the address packets.

At a time E8, the CLE signal (wave form 906) is again activated toenable the first and second memory chips to read command signals. At atime E9, the first flash signal (wave form 902) transmits DOH, which isan ‘erase confirm command’ to the first flash memory chip. This command,as sampled by the CLE signal, actually initiates the erase operationwithin the flash chips, after which, the contents of data fields 734 and738 of each memory row portion 732 of the addressed sub-block 730 (FIG.7) of the first flash memory chip 670 are erased, i.e. set to an “all1's” state. At a time E1, the FRDY-BSY* signal (wave form 912)transitions from a HIGH state to a LOW state to indicate to the flashstate machine 642 (FIG. 6) that at least one of the flash memory chipsis busy.

At a time E11, the CLE signal (wave form 906) is activated to enable thefirst and second flash memory chips to read command signals. At a timeE12, the first and second flash signals (wave forms 902 and 904) eachtransmit a command signal. The first flash signal (wave form 902)transmits a read command signal 70H via the first split bus 680 (FIG. 6)to the first flash memory chip while the second flash signal.(wave form904) transmits an erase command signal 60H via the second split bus 684(FIG. 6) to the second flash memory chip. At a time E13, while thecommand signals 70H and 60H are active, the WE signal (wave form 910)transitions to the LOW state to enable the first and second flash memorychips to read the command signals 60H and 70H. At a time E14, the CLEsignal (wave form 906) is deactivated to disable the flash memory chipsfrom reading command signals and the ALE signal (wave form 908) isactivated thereby enabling the first and second flash memory chips toread packets of address information. At times E15 and E16, the secondflash signal (wave form 904) transmits first and second address packetsADD0 and ADD1 respectively to the second flash memory chip wherein thefirst and second address packets ADD0 and ADD1 specify a sub-block 731(FIG. 7) of the second flash memory chip 672 of the memory bank. At atime E17, the ALE signal (wave form 908) is deactivated. During timeintervals between times E13 and E14, and E14 and E15, the WE signal(wave form 910) enables the flash memory chips to read the addresspackets. At a time E18, the CLE signal (wave form 906) is againactivated to enable the first and second memory chips to read commandsignals. At a time E19, the first flash signal (wave form 902) transmitsDOH to the first flash memory chip to erase the contents of data fields734 and 738 of each memory row portion 732 of the specified block andthereby set them to an “all 1's” state.

To summarize, during a time interval TEB 1, between the times E0 andE11, the memory controller erases an addressed sub-block 730 (FIG. 7) ofthe first flash memory chip 670. Also, during a time interval TEB2,between the times E11 and E20, the memory controller erases acorresponding addressed sub-block 731 (FIG. 7) of the second flashmemory chip 672. At a time E21, the FRDY_BSY* signal (wave form 916)transitions from a LOW state to a HIGH state to indicate to the flashstate machine 642 (FIG. 6) that both of the flash memory chips arefinished with the erase operation.

Immediately after time E21, the first and second flash signals (waveforms 902 and 904) each transmit a read status command signal 70H to thefirst and second flash memory chips respectively. While the read commandsignals 70H are active, the WE signal (wave form 910) transitions to theLOW state thereby enabling the first and second flash memory chips toread the read command signals 70H. At a time E22, the first and secondflash signals (wave forms 902 and 904) both transmit a status data backto the controller.

So, the status of both flash memory chips are read simultaneously afterthe erase operation is performed on the two corresponding addressedsub-blocks of the flash memory chips as described above.

If either of the sub-blocks 730, 731 of the memory chips has an error,the entire block 727 (FIG. 7) within the chips is marked defective bysetting the contents of the defect flag 756 (FIG. 7) in the second flashmemory chip 672.

FIG. 15 is a flowchart illustrating a process of erasing a block,including a first sub-block stored in a first memory unit and a secondsub-block stored in a second memory unit, in accordance with the presentinvention. Microprocessor 620 (FIG. 6) executes instructions, which arestored in code RAM 626 (FIG. 6) to carry out the depicted process.

In step 1502, microprocessor 620 (FIG. 6) loads a block address to beerased. In step 1504, the microprocessor initiates the erase operationsdescribed above in reference to the timing diagram at 1400 (FIG. 14). At1506, the microprocessor determines whether the erase operation isfinished by reading the flash ready/busy (FRDY_BSY*) signal (wave form916 of FIG. 14) which transitions from a LOW state to a HIGH state toindicate to the flash state machine 642 (FIG. 6) that both of the flashmemory chips are finished with the erase operation. At 1508, themicroprocessor reads the status of the flash chips 670, 672 (FIG. 6). At1508, the microprocessor determines whether the erase operationperformed in step 1504 was successful in both of the flash chips 670,672 (FIG. 6) and, if so, the process ends. If it is determined that theerase operation performed in step 1504 was not successful in both of theflash chips, then the microprocessor marks the block in both of theflash chips 670, 672 defective.

Although the present invention has been described in terms of specificembodiments, it is anticipated that alterations and modificationsthereof will no doubt become apparent to those skilled in the art. It istherefore intended that the following claims be interpreted as coveringall such alterations and modification as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A memory storage system for increasing theperformance of write operations of sector information to storagelocations within nonvolatile memory unit, said nonvolatile memory unitincluding one or more nonvolatile memory devices, the sector locationsorganized into sub-blocks, each sub-block including more than one sectorand each sub-block being individually addressable and erasable and aplurality of sub-blocks defining a block comprising: memory controlcircuitry, coupled to the nonvolatile memory unit, responsive to sectorswhich each include sector information, received from a host, saidreceived sectors being identified by sectors numbers of a predeterminedorder, said memory control circuitry for writing sector information,received from the host, to a first sector location of a particularsub-block of a particular block, said particular block being identifiedby the same virtual physical block address (VPBA) and assignable basedupon the identification of a free location within said memory unit, saidmemory control circuitry for further writing sector information,received from the host, to a first sector location of a sub-block of theparticular block that is other than the particular sub-block andregardless of the predetermined order of the sector numbers of thereceived sectors, wherein writing of sector information to the firstsector locations of the sub-blocks of the particular block are performedsubstantially concurrently thereby increasing the performance of writeoperations.
 2. A nonvolatile memory system as recited in claim 1 whereineach sub-block of the block is located in a different nonvolatile memorydevice thereby allowing substantially concurrent write operations to beperformed on the sub-blocks of the particular block that span more thanone nonvolatile memory device.
 3. A nonvolatile memory system as recitedin claim 1 wherein a virtual physical block address (VPBA) identifiessub-blocks of the particular block.
 4. A memory storage system forincreasing the performance of write operations of sector information tostorage locations within nonvolatile memory unit, said nonvolatilememory unit including one or more nonvolatile memory devices, the sectorlocations organized into sub-blocks and a plurality of sub-blocksdefining a block comprising: memory control circuitry, coupled to thenonvolatile memory unit, responsive to sectors which each include sectorinformation, received from the host, said received sectors beingidentified by sector numbers of a predetermined order, said memorycontrol circuitry for writing sector information, received from thehost, to a first sector location of a particular sub-block of aparticular block, said memory control circuitry for further writingsector information, received from the host, to a first sector locationof a sub-block of the particular block that is other than the particularsub-block and regardless of the predetermined order of the sectornumbers of the received sectors, a single virtual physical block address(VPBA) assignable based upon the identification of a free locationwithin said memory unit and for identifying the sectors of saidsub-blocks of the particular block, wherein writing of sectorinformation to the first sector locations of the sub-blocks of theparticular block are performed substantially concurrently therebyincreasing the performance of write operations.